Phase shifter



ug- 11, 1953 l H. SOHON ET AL 2,648,811

PHASE SHIFTER Filed July 2o,A 1948 4 #mf-Afm wf/hamm mmm) @1f/62 AMELPatented ug. 11, 1953 UNITED STATES PATENT OFFICE.

Baker; Moorestown; N. Ji, assgnors to' Radio Corporati'omof A'm'erica, acorporation of-D`ela Wavre Application JVIIIXZO, 1948SrialN0. 39,714

3 -Claims;

. 1; Oury invention relates' to electrical apparatus and'more'specicallyto -anovel dev-ice which will shiftthe phase of analternatingvoltage.

Elaborate apparatus heretofore proposedV for shift-ing phase hasbeenprohibitive-in costi and in many cases could not bei usedpractically-a Belicate adjustmentsand` fragilityl havefalso limitedthescopel-ot` use-'of prior phase-shitters; Furthermore, many phase-shifters ofthe-prior; art have been dependent'- upena function' offrequency for their operation because Atheyhaveused inductances andcapacities andi therefore have presented dierentl characteristics when'-operated at different frequencies; These frequency limitationsl have-ffur-ther necessitatedi unique design principles forl special phase.shifting eiects and have necessitated complex networks for; multi.-Aphasevuse. The simpler phaseshifting devices ofy the priorart do notprovidel aconstant-output voltage over an entire 360% of. phase'fshift..In many. applications: of; such. phase; Shifters a change ofi outputvoltage.withphaseishift; is.in tolerable.

Itis accordingly an. objects of. our, invention, to provide aAsimplified method fori-shifting.. phase which. will produceaconstantoutput voltage, over 350i phase. shit,.the amplitudev of whichising dependentof .frequency or. phase shift.

Another object of; our-invention is; Jtofmake a cheaply.constructed:andimechanically. stable de- Vicewhichwill change phaseover: anventire angle .of.36(l, .and in wlflichthe phase change,` is.directly proportonal. to the.y angular displacement of a rotatableAarm, without. the` use of a. specially wound and expensivepotentiometer.

Ai further object is. to providea simple means Afor. shifting. of a`rnultiphaseV voltage and for selecting the desired phase; angle with.oneconftrol.

,A still further object of our invention is to provide for a simplieclmeans of obtaining special or non-linear phase characteristics.l

Briey., realization ofy these. objects is. attained .in one speciiic.embodiment of our invention. by

providing a pairv of specially designedpotentiometers consisting ci datg uniform resistance' strips of carbon, orother such resistancematerial; having two alternating voltages of'difierent phase connectedrespectively across them. A voltage 'of' variable phase is takenfrom'two gan'gedf' ro*- ltatable arms which makecontactattheir radial'extremities to'the strips;

This voltage-is oiz constant amplitude and=ofvphase relationship-pro-'po-rtional to the angular displacement of." the Cil arms. Multiephase.outputvoltagef may, be. real:` f

ized by adding additional contact arms, and

2. special? phase characteristics` mayv be obtained: by changingresistor or slider ar-mcharacteristics.

Features of our invention which we consider novelare set:V forthwith.particularity in the appended claims. The invention itself, however,both as-to its organization and its methods of operation, together withadditional objects and advantages, will best be understood from thefollowing description of: a .specicembodimenu when read in connectionwith the accompanying drawing; in which:

Figures 1 andr 2L show diagrammaticallyl-a preferred embodiment-of twodelements which make up-the phase' shifter.

Figure 3 shows a phase shifter assembled according to the invention:

Figure Ll isa modiiication of Figure 3,. and

Figure 5 illustrates an alternate means ofV connecting the phaseshifter.

Asis-shown in Figur-e lgtheresistance element in-thepjotentiometerconsists of' a square orrectangular strip, towhich voltage of phase Aisimpressed.. at the end.terminals,. 2` and 3. The impressed voltage istaken from an input source, 4, which hasa tap, I3at the approximatecenter. A slider arm, 5, makes Contact with theresistance stripA at itsradial extremity andlis moved. in a circular path with. its center atVor. near the center of the strip and with. angular. displacement,`fromthe line air-:c2 which may beV called the angle. 0. Output voltage, ei,is takenbetween the slider arm and the tap, I3, on. the input source.

The resistanceyelementgt, showndn Figure 2 is identical with that shownin Figure 1 with voltage of phase-B impressed'- atV its"V end terminals,'1fand 8, comingfrom avoltagescurce,- 9.V Displacement of its slider,vi0, isn'ovf the angle (Gil-00- and a voltage, e2,-

developedfl betweent the slider.' arm and the f: tap, I 4 on'v thevvoltage; source:

The two elements are: combinedJ inl- Figure-r, 3 by connections betweenthe tapson. therespec.- tive voltage#sources;` Outputvoltage; en -e2, ofvariable phase is taken in push-pull from between the slider arms, 5 andIU.

In Figure 4- oneof the resistance strips,` is orientated! at an-anglea-A(which is in this case Y9.09). tothe other stripf, I, morder. tofallowthe functional position of the slider. arms, Elandl I E3',,to beparallel for simplied construction. Electrical connections'arem'adeydirectly'-betweenpoints, I 5 and` I 6i onthe resistance stripscorresponding totapsfinvthe voltage input. Contact arms on ther two;strips areganged,

Figure 5 provides a circuit for push-push connection of the voltages e1and e2 to give an out- 3 put voltage ei-l-ez. This is accomplished bytaking the first side of the voltage from a common transformer tapconnection and the second side from a common slider arm connection. Tworesistors, Ii and I2, are inserted between the respective slider armsand the second common output voltage connection.

Operation of the phase shifter is explained in the following discussion.The voltage e1 in Figure l is effectively the voltage drop between thecenter line, :z3-x', of the potentiometer and the point of slider armcontact and may be expressed as e1:E sin 0 sin wt where 0 is the anglethrough which the slider arm has lbeen moved and w is the angularvelocity of the supply voltage.

The voltage e2 in Figure 2 is similarly expressed as ezzE sin 1]/ sin(wt-a) where a is the time angle between, the two phases of the Voltagesource and H20-Hu.

Letting (1:90", which is convenient for both electrical phasing andmechanical arrangement, the voltages become:

e1=E sin 0 sin witzl/z E cos (wt-)-1/ E cos (wt-i-a) 22E sin (H4-90) Sin(wt-90):-E

cos 0 cos wt and 1/2 E cos (wt-0) -1/2 E cos (wt-F0) When the midpoints,or other points corresponding to the center of the slider arms, of thetWo phases are connected together as in Figure 3 the output voltagetaken between the sliders will be:

e1ez=E cos (wt-0) It is seen that this Voltage is of constant amplitude,E, and of phase proportional to the angle 9.

By assembling the two potentiometer elements at the angle a, in thiscase 90, as shown in Figure 4, the sliders may be placed in the samedirection on the shaft, for convenient mechanical construction.

The two potentiometers are connected with their outputs in push-pushinstead of push-pull in Figure 5 in which case the resistors, l l andI2, are connected between the slider arms and the common outputconnection to prevent short circuit of the output voltage. In thiscircuit the output voltage is the sum of the component voltages e1 ande2 being:

which voltage is also of constant amplitude E and of variable phaseproportioned to the angle 0. If for any reason the input Voltage phasesare not 90 apart in time, (a+90) the result is still a constant Voltageof variable phase proportional to the angle 0. In this case e1=E sin 0sin wt :1/2 E cos (wt-6) -1/2 E cos (wt-H9) and With a push-pullconnection as in Figure 4 the voltage difference is vei-ezzl/Z E cos(wt-0)-1/2 E cos When the connection is made in parallel, however, as inFigure 5, the angle ,lf should equal 180+0a and then @12E sin 0 sinwtzl/Z E cos (wt-0) 1A.; E cos (wt-i-) e2:E sin (1804-0-10 sin (wt-a) :lE cos (wt-0)|1/2 E cos (wt+0-2a) The sum is now:

It is to be noted that for the push-pull connection gif- (-a) and forthe parallel connection i:180+(0-a). When changing from series toparallel connection the correct angular adjustment is obtained byinterchanging the wires connected to one potentiometer.

Theoretically, the resistance strips should be `uniform and continuous,however, for ease of construction it is reasonable to pierce the stripso that the potentiometer shaft can be passed through. The errorintroduced by this hole is small if its radius is small compared to theradius of the circular track which the slider arm follows.

Additional phases can be obtained from the shifter merely by placingadditional arms on the potentiometers, and their phase relationship willbe determined by the angular displacement with respect to the initialarms.

Special phase shifting characteristics may be obtained by makingnon-circular contact arms, special resistance elements, variable stripshapes, or variable voltage feed points.

Because the working elements of our phase shifter are resistanceelements, their voltage amplitudes are constant at all frequencies andhence there are no critical adjustments or tolerances in this device,construction is cheap and simple, and the strips may be made towithstand considerable vibration or jolting.

Having thus fully described the nature, construction and operation ofour invention, we wish to secure by Letters Patent, and claim:

l. Phase shifting apparatus comprising, in combination; a first block ofresistance material having a fiat uniform face, a first rotatablecontact arm having one end attached substantially in the center of saidflat face, the other end of said contact arm being of such a length andso shaped as to contact said face throughout a 360 rotation of said arm,a second block of resistance material having a flat uniform face. asecond rotatable contact arm attached to the second block similarly tosaid first contact arm, a rst alternating voltage connected acrossopposite ends of said first block, a second alternating voltageconnected across opposite ends of said second block, said alternatingvoltages being of different time relationships, an electrical oonnectionbetween said sources of alternating voltage and a pair of outputterminals connected between the contact arms.

2. Phase shifting apparatus comprising, in combination; a first block ofresistance material having a flat uniform face, a first rotatablecontact arm having one end attached substantially in the center of saidflat face, the other end of said contact arm being of such a length andso shaped as to contact said face throughout a 360 rotation of said arm,a second block of re sistance material having a flat uniform face, asecond rotatable contact arm attached to the second block similarly tosaid first contact arm, a first transformer having primary and secondarywindings, a rst alternating voltage connected across the primary of saidfirst transformer, a

ondary windings, a second alternating voltage connected across theprimary of said second transformer, said voltages being of diiferenttime relationships, an electrical connection between the center tap ofthe secondary Winding of said iirst transformer and the center tap ofthe seoondary Winding of said second transformer, and a pair of outputterminals connected between the contact arms.

3. Phase shifting apparatus comprising in combination; a rst block ofresistance material having a fiat uniform face, a first rotatablecontact arm having one end attached substantially in the center of saidat face, the other end of said contact arm being of such a length and soshaped as to contact said face throughout a 360 rotation of said arm, asecond block of resistance material having a ilat uniform face, a secondrotatable contact arm attached to the second block similarly to said rstcontact arm, a first alternating voltage connected across opposite sidesof said rst block, a second alternating voltage connected acrossopposite sides of said second block, said alternating voltages being ofdiierent time relationships, an electrical connection from theapproximate center of a third side of said rst block to the approximatecenter of a third side of said second block, and a pair of outputterminals connected between the contact arms.

HARRY SOI-ION. HARRY F. BAKER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,241,615 Plebanksi May 13, 1941 2,411,030 Ryder Nov. 12, 19462,434,057 Sproule Jan. 6, 1948 2,457,178 Richardson et al. Dec. 28, 19482,469,183 Werner May 3, 1949 2,483,125 Cummerow Sept. 27, 1949 2,515,236Kunins July 18, 1950 FOREIGN PATENTS Number Country Date 451,786 GreatBritain Aug. 12, 1936 OTHER REFERENCES Publication, Instruments, Apr.1937, vol. 10, pp. 104 and 105.

